There are many systems available and in use for efficiently loading and unloading truck trailers with relatively uniform types of freight. For example, if a trailer is loaded with only hand liftable cartons, the trailer may be unloaded entirely manually, as onto pallets on a dock; or a conveyor may be extended into the trailer and the cartons manually placed onto the conveyor. Similarly, if a trailer is loaded with only palleted freight, it may be unloaded fairly efficiently using a conventional fork lift truck.
In some trucking operations, particularly larger general freight carriers, a great variety of freight may be shipped from a number of diverse origins to a central facility for local or distant transshipment. At the central facility, freight from the arriving trucks is unloaded, sorted according to destination, then reassembled into loads in such a manner as to most economically utilize the trucks. Because of the nature of this kind of shipping operation, trucks often arrive at a central facility with mixed freight loads, hand liftable articles interspersed with palleted freight and other types of bulky or heavy articles which are not suitable for manual unloading. Such mixed freight loads are often referred to as "LTL" freight for "Less (than) Truck Load".
In the past, the utilization of labor and equipment in loading and unloading such LTL trailers has often been inefficient and uneconomical. Because of the indeterminate mix of manually liftable freight and freight requiring mechanized handling and possible uncertainty of arrival times of trucks, it is often difficult to provide an optimum combination of labor and equipment for unloading such trucks to assure that the laborers are not overworked at certain times and left idle at others. On some docks, only certain designated persons ma be permitted to operate fork lift trucks. Also, a single fork lift truck or conveyor may be required to service multiple dock positions. As different types of freight are encountered in loading or unloading the trailer, workers are often left standing about idly as equipment is awaited and changeover thereof occurs. If conveyors are employed in the trailers for manually liftable articles, time and effort are consumed in extending and retracting the conveyors when a fork lift is required to handle heavier freight.
In loading truck trailers with mixed types of freight for offloading at several locations, it is desirable to position the freight in such a manner as to minimize handling at each stop. Thus, a load for a first stop is positioned rearmost in the trailer, and a load for a last stop is positioned toward the front of the trailer. Problems similar to those encountered in unloading mixed freight occur in loading mixed freight onto trailers.
The results of such inefficiency, among other disadvantages, are that dock workers and unloading equipment are inefficiently employed, and the docks and truck trailers are tied up awaiting loading or unloading. Shipping costs are thereby increased and profits to the warehousing facility and/or trucking company are diminished.